1. Technical Field
The present invention relates to a charging roller, an electrophotographic process cartridge, and an image forming apparatus.
2. Related Art
Image forming apparatuses utilizing an electrographic system allows high-speed and high-quality printing, thus have been used in copying machines, laser beam printers, and other machines. In an image forming apparatus utilizing an electrographic system, a uniform electric charge is formed on the surface of an electrophotographic photoreceptor, and an electrostatic latent image is formed by an LED, laser, or the like, thereafter the electrostatic latent image is developed with charged toner into a toner image. Further, the toner image is transferred to a recording medium, such as paper, via an intermediate transfer medium or directly using electrostatic, and thereby a desired image is formed.
As described above, an image forming apparatus utilizing an electrographic system involves a charging process for forming a uniform electric charge on the surface of an electrophotographic photoreceptor, wherein the electrophotographic photoreceptor is charged by a non-contact or contact charging method. Commonly a non-contact charging method uses a corotron or scorotron, and a common contact charging method uses a roll, brush, sheet, or the like. Since in contact charging methods generally, the applied electric current is smaller, they thus generate significantly smaller quantities of ozone than non-contact charging methods.
In printers used at offices and homes, consumable parts which require replacement, such as electrophotographic photoreceptors and toner, may be of cartridge type for easy replacement. These easily replaceable cartridges are required to have a longer life in order to reduce the frequency of replacement, reflecting recent environment issues. For extending the life of a cartridge containing an electrophotographic photoreceptor, it is necessary to extend the life of the electrophotographic photoreceptor and units incorporated in the electrophotographic photoreceptor, such as a unit for charging the electrophotographic photoreceptor, an image input unit for forming an electrostatic latent image on the electrophotographic photoreceptor, a development unit for developing the electrostatic latent image with a developer into a toner image, a transfer unit for transferring the toner image to a receiving medium, and a cleaning unit for removing the residual developer remaining on the electrophotographic photoreceptor after transfer.
When the electrophotographic photoreceptor is charged with a charging unit using a direct current alone, abrasion of the electrophotographic photoreceptor can be suppressed and the electrophotographic photoreceptor can be used for a longer term. The charging unit often has an intermediate layer and a migration preventing layer provided on the surface of a resistive layer, for preventing bleeding and blooming. The resistive layer is often ground into a precise shape, in order to ensure uniform contact between the charging unit and electrophotographic photoreceptor. The grinding treatment is usually conducted with a grinding stone.